Specific Process Knowledge/Etch/Etching of Chromium

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Etching of Chromium

Etching of chromium can be done either by wet etch, dry etch or by sputtering with ions.

• Etching of Cr by wet etch
• Etching of Al by dry etch
• Sputtering of Al

Comparison of Aluminium Etch Metodes

	Al wet etch 1	Al wet etch 2	Al etch by ICP metal	Al sputtering by IBE (Ionfab300+)
Generel description	Wet etch of pure Al	Wet etch of Al + 1.5% Si	Dry plasma etch of Al	Sputtering of Al - pure physical etch
Etch rate range	~100nm/min (pure Al)	~60nm/min (Al+1.5% Si)	~350 nm/min (depending on features size and etch load)	~30nm/min (not tested yet)
Etch profile	Isotropic	Isotropic	Anisotropic (vertical sidewalls)	Anisotropic (angles sidewalls, typical around 70 dg)
Substrate size	#1-25 100 mm wafers	#1-25 100 mm wafers	smaller pieces on a carrier wafer #1 100mm wafers (when set up to 100mm wafers) #1 150mm wafers (when set up to 150mm wafers)	Smaller pieces glued to carrier wafer #1 50mm wafer #1 100mm wafer #1 150mm wafer #1 200mm wafer
Allowed materials	Aluminium Silicon Silicon Oxide Silicon Nitride Silicon Oxynitride Photoresist E-beam resist	Aluminium Silicon Silicon Oxide Silicon Nitride Silicon Oxynitride Photoresist E-beam resist	Silicon Quartz/fused silica Photoresist/e-beam resist PolySilicon, Silicon oxide Silicon (oxy)nitride Aluminium Titanium Chromium	Silicon Silicon oxides Silicon nitrides Metals from the +list Metals from the -list Alloys from the above list Stainless steel Glass III-V materials Resists Polymers Capton tape

Ething of Chromium can be done either wet or dry. For wet etching please see below on this page. Dry etching can be done either with ICP using Chlorine chemistry or with IBE by sputtering with Ar ions.

Wet etching of Chromium

Fume hood: positioned in cleanroom 2.
Wet Etch of Chromium can take place in a beaker in this fume hood

Wet etching of chromium at Danchip is done making your own set up in a beaker in a fume hood - preferably in cleanroom 2 or 4. We have two solution for this:

1. HNO₃:H₂O:cerisulphate - 90ml:1200ml:15g - standard at Danchip
2. Commercial chromium etch

Etch rate are depending on the level of oxidation of the metal.

How to mix the Chromium etch 1:

1. Take a beaker and add 15g of cerisulphate.
2. Add a little water while stirring - make sure all lumps are gone.
3. Add water until 600 ml - keep stirring (use magnetic stirring)
4. Add 90 ml HNO₃
5. When the cerisulphate is completely dissolved (clear liquid) you can add the other 600 ml of wafer.

Overview of the data for the chromium etches

	Chromium etch 1	Chromium etch 2
General description	Etch of chromium	Etch of chromium
Chemical solution	HNO3:H2O:cerisulphate - 90ml:1200ml:15g	.
Process temperature	Room temperature	.
Possible masking materials	Photoresist (1.5 µm AZ5214E)	.
Etch rate	~40-100 nm/min	.
Batch size	1-25 wafers at a time	.
Size of substrate	4" wafers	.
Allowed materials	No restrictions. Make a note on the bottle of which materials have been processed.	.

Dry etching of chromium

On the ICP Metal Etch tool a recipe for chromium is being developed.